Polyester resin composition having a thickening agent therein



March 4, 1969 BAUM ET AL 3,431,320

POLYESTER RESIN COMPOSITION HAVING A THICKENING AGENT THEREIN Filed Dec. 11. 1967 UNSATURATED COPOLYMERIZABLE MONOMER 03,5 ETHYLENICALLY UNSATURATED MONOMER POLYESTER RESIN OPTIONAL HIGH TEMPERATURE FREE RADICAL INITIATORS AND ACCELERATORS CALCIUM HYDROXIDE OR MAGNESIUM OXIDE CALCIUM OXIDE THICKENED, UNCURED POLYESTER RESIN INVENTORS MEL VINE. 5411M, FRANK FKET BY JOHN A. HATw/v United States Patent 3,431,320 POLYESTER RESIN COMPOSITION HAVING A THICKENING AGENT THEREIN Melvin E. Baum and Frank Fekete, Monroeville, and John A. Hatton, Verona, Pa., assignors to Koppers Company, Inc., a corporation of Delaware Filed Dec. 11, 1967, Ser. No. 689,595 US. Cl. 260-865 Int. Cl. C08f 21/00 6 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Cured unsaturated polyester resins which have been reinforced by fibrous materials such as glass fiber mats or the like have excellent physical strength characteristics. However, the formation of shaped objects with such materials has presented problems because the fibers initially immersed within the uncured liquid resin tend to rise to the surface causing the object, after curing of the resin, to have irregularities in the surface.

To avoid this problem, preforms have been made by spraying glass fibers onto screens similar in shape to the final desired product. Air is sucked through the screen to hold the fibers in place. A binder is then sprayed over the fibers and cured to hold the fibers together in the desired form. The form is then placed into a mold and the unsaturated polyester resin is poured into the mold and cured therein. The resin must be viscous enough to adhere to the form, yet not so viscous as to prevent proper wetting of the fibers.

To overcome the foregoing cumbersome and critical process, it has been proposed to coat the glass fibers with the uncured unsaturated polyester resin liquid to thoroughly wet the fiber. The liquid resin is then thickened, without actually curing the resin by chemical or physical means. The physical means include: (1) driving oif a volatile solvent in which a viscous polyester resin has been dissolved, or (2) using a heated viscous polyester resin and then cooling the coated fibers after application. The chemical means include: (1) the addition of a thickening agent such as MgO to the polyester resin, or (2) the partial copolymerization or curing of the resin to a gelled or B-stage. Fibrous reinforcements can thus be pre-coated with a low viscosity thickenable polyester resin which will therefore properly wet the fibers, yet the polyester resin coatings will rapidly lose its tacky state by the increase in viscosity enhancing the storability of the precoated fibers. Thus, the use of preforms is eliminated as well as the attendant mess of coating the irregular-shaped preform with a liquid resin. Glass fiber mats coated with such resins may be easily handled and charged to molding machines. More positive control of the amount of charge as well as the shape of the charge can thus be maintained resulting in higher quality molded products as well as economic savings.

However, such systems each have certain economic drawbacks. The solvent system, of course, results in loss of the solvent plus disposal of the fumes. Heating viscous polyesters to reduce their viscosity is costly and cumbersome. Chemical thickening the polyester resin such as by the addition of MgO or Ca(OH) as shown in US. Patent 2,568,331 issued to Vincent Frilette results in an eventual viscosity build-up; however, one of its drawbacks is that the initial thickening rapidly builds up the viscosity which reduces the pot life of the resin. Another diflic-ulty encountered is the slow overall build-up of the viscosity of the resin. On the other hand, resins modified to rapidly cure to the B-stage have a tendency to continue to cure or harden beyond the B-stage within a short period of time. The B-stage actually represents an intermediate stage of the vinyl copolymerization or curing of the resin.

SUMMARY OF THE INVENTION It has now been discovered that chemical thickening of polyester resins by the addition of Ca(OH) or MgO can be greatly enhanced by the addition of CaO. This addition results in an inhibition of viscosity build-up for several hours and thereafter causes a rapid high viscosity build-up which can result in viscosities as much as 8 times that obtained using the previously known chemical thickening agents. The invention thus allows the pot life of the resin to be extended yet provides a rapid high viscosity build-up after the initial inhibition of viscosity mcrease.

In accordance with the invention, an unsaturated polyester resin composition which increases in viscosity after formation of the composition comprises: (a) an unsaturated polyester formed by condensing at least one dicarboxylic acid containing cap-ethylenic unsaturation, and a dihydric alcohol; (1)) an mdethylenically unsaturated copolymerizable monomer; and (c) a thickening agent that will increase the viscosity of the composition after a spaced period of time, the thickening agent consisting essentially of a combination of calcium oxide and either calcium hydroxide or magnesium oxide.

This discovery was quite surprising in view of the fact that the addition of CaO by itself does not result in thickening. Apparently the CaO has a synergistic eifect upon the Ca(OH) or MgO which results in the two eflfects of initially slowing down the viscosity increase and yet magnifying the eventual viscosity increase.

DETAILED DESCRIPTION As previously described, in accordance with the invention, an unsaturated polyester resin may be thickened by the addition of a combination calcium oxide and either magnesium oxide or calcium hydroxide to initially inhibit viscosity build-up (thus giving a longer pot life) and then rapidly increasing the viscosity of the resin.

Unsaturated polyester resins are well known in the art (see, for example, US. Patent 2,255,313, issued to Carleton Ellis). The unsaturated polyester is a condensation polymer formed by polyesterifying dicarboxylic acids with dihydric alcohols. To form the polyesters approxirnately equalmolar proportions of the dicarboxylic acids and dihydric alcohols are used. To provide unsaturation within the polyester, at least a portion of the dicarboxylic acid contain ethylenic unsaturation. Examples of such ethylenically unsaturated dicarboxylic acids include maleic and fumaric acids. The remainder of the dicarboxylic acids are usually either saturated normal aliphatics such as adipic acid, succinic acid, or the like, or aromatic diacids such as phthalic acid, isophthalic acid or the like as well as their halogenated derivatives such as tetrachlorophthalic anhydride or the like.

Illustrative of the dihydric alcohols are ethylene glycol, propylene glycol, l,2-butanediol, 1,3-butanediol, 1,4-butanediol, diethylene glycol, polypropylene glycol, 2,2 -dimethyl-l, 3-propandiol, 1,4-cyclohexane dirnethanol and adducts or reaction products of alylene oxides with 2,2- bis(4-hydroxy phenylene) propane (Bis-phenol A).

The dicarboxylic acids and dihydric alcohols are reacted together in approximately equimolar proportions to form a polyester. The average molecular weight of the polymer is most conveniently measured with respect to the acid end groups. A gram of the polyester is titrated with KOH and the number of milligrams of KOH necessary to neutralize the gram of polyester is called the acid number of the polyester. Acid numbers below 100 usually signify polyesters having sufficient molecular weight to possess good physical properties. Therefore, the unsaturated polyesters useful in the invention are those possessing a molecular weight indicated by an acid number below 100.

After formation, the unsaturated polyester is usually dissolved in an c lt-ethylenically unsaturated monomer such as styrene or vinyl toluene. The amount of monomer used generally is about 10-60% and preferably 2050% by weight of the total polyester resin. The unsaturated polyester resin (polyester and monomer) is then cured by initiating a free radical polymerization between the ethylenically unsaturated monomer and the unsaturated polyester at the a,,8-6thYl6I1iC double bonds in the polyester. This copolymerization may be initiated by UV light or radiation, but is more commonly initiated by addition of a peroxide catalyst followed by heating. The polyester resin copolymerizes to form a cross-linked thermoset resm.

Illustrative of the copolymerizable ethylenically unsaturated monomers are styrene, a-methylstyrene, chlorostyrene, vinyl toluene, divinyl benzene, diallylphthalate, methyl methacrylate and the like.

Examples of peroxide catalysts commonly used to initiate the copolymerization include benzoyl peroxide, methylethyl ketone peroxide, cumene hydroperoxide, and the like. Other free radical generating catalysts may also be used as, for example: 2,2-azobisisobutyronitrile. Preferably the catalyst system selected is one which is inactive at room temperature since the invention contemplates a desired use of a thickenable, yet unpolymerized resin which retains the flexibility of an uncured resin.

In accordance with the invention, the viscosity of the polyester resin is increased before the final curing of the resin by the addition of novel chemical thickeners which retard rapid viscosity build-up for about several hours and thereafter rapidly raise the viscosity of the resin. This enables workmen in the field to coat, for example, glass fiber mats with the polyester resin compositions of the invention over a longer period of time without fear of premature thickening of the composition within the resin pot which might otherwise necessitate discarding resin too thick to efficiently remove from the pot or, at best, might result in improper wetting of the glass fibers. The composition of the invention not only provides a slower initial viscosity build-up, but provides a rapid and high build-up after a period of about 24-48 hours. This allows workmen, for example, to stack previously coated glass fiber mats after several days in contrast to prior art chemically thickened compositions which may remain sticky for several days to a week.

As will be demonstrated hereafter in the examples, polyester resins thickened in accordance with the invention exhibit such a high overall viscosity increase that after 8 days the viscosity is many times the viscosity attained during the initial 24 hours. This is in marked contrast to the prior art systems thickened with only MgO or Ca(OH) in similar proportions. Such systems do not exhibit the high ratio of viscosity increases. This characteristic is very important bearing in mind that the object of any viscosity thickening system is to provide a resin of initial low viscosity which will attain eventual high viscosity. To attempt to achieve the high viscosity results of the system of this invention by the use of MgO' or Ca(OH) alone would result in a system having too high an initial viscosity for practical use.

In accordance with the invention, a mixture of calcium oxide and either magnesium oxide or calcium hydroxide is added to the unsaturated polyester resin before application of the resin to a substrate or fiber mat or the like. The salts may be added before, during or after the addition of the peroxide catalysts commonly used in such systems.

The amount of the inorganic salts and the ratios therebetween may vary somewhat depending upon the amount of viscosity build-up desired. It has been found, however, that the calcium oxide must be used in a minimum amount of at least 1% and preferably 2% by weight of the polyester resin. When magnesium oxide is the second salt, it must be used in a minimum amount of at least 1.5% by weight of the polyester resin. When calcium hydroxide is the second salt it is used in a minimum amount of 2.0% by weight of the polyester resin. While larger amounts of either salt may be used, it has been found that total amounts adding up to greater than about 6% are unnecessary to achieve the rapid and high viscosity chemical thickening of the invention.

It should be noted that the chemical thickening referred to herein is not a gelatin or B-stage of the resin. Such gelatin or B-stage is indicative of commencement of the vinyl copolymerization between the unsaturated portion of the condensation polymer and the ethylenically unsaturated monomer. Polyester resin chemically thickened in accordance with the invention can be completely dissolved off a glass fiber mat impregnated with the resin with acetone. Gelled or B-stage polyester resins are not entirely soluble in acetone which is indicative of the presence of vinyl copolymerization.

The invention will be further understood by referring to the attached fiow sheet and the following examples.

Example I 100 gram samples of polyester resin were prepared by diluting Koplac 2000 (a commercial polyester made by condensing maleic anhydride and phthalic anhydride with propylene glycol in mole ratios of 1:1:2 to an acid number of about 30) with monomeric styrene to a by weight polyester 30% by weight monomer content. Various amounts of CaO and Ca(OH) were added respectively to each sample and the viscosity change noted. The results are tabulated below:

TABLE I Percent Percent V Sample No CaO oarorr 2 Initial lscoslty m em 1 hr. 3 hrs 5 hrs. 24 hrs. 168 hrs 0 5. 0 1, 650 25, 500 75, 000 116 000 380 000 l 2. s 0 1, 650 t 0 3. 0 2. 0 1, 650 1, 500 1, 600 2,100 650, 000 8. 6 2. 0 3. 0 1, 650 1, 550 5, 900 120, 000 1 1.15 l 8. 0 1. 0 4. 0 1, 650 1, 850 68,000 150,000 550, 000 l 5. 1 4. 5 2. 0 l, 650 1, 500 1, 650 1, 800 760, 000 1 17. 0 3. 8 2. 9 1, 650 1, 650 2,000 76, 000 l 25. 0

1 Million.

The table illustrates the surprising results obtained by the mixture of salts. While CaO provides no sginificant thickening when used by itself, the Ca(OH) when used alone quickly thickens the polyester resin. Yet the combination of the two salts lowers the initial thickening but Thus, the use of preforms is eliminated as well as the attendant mess of coating the irregular-shaped preform with a liquid resin. Glass fiber mats coated with the resin of the invention may be easily handled and charged to molding machines. More positive control of the amount yields much higher viscosity which are noted already at 5 of charge as well as the shape of the charge can thus 24 h It h ld l b t d that hen only 1% be maintained resulting in higher quality molded products. CaO is used the results are markedly less than when at What is claimed is: l t 2% i d Th 2% i th efe d mi i m 1- 1. An unsaturated polyester resin composition which though even the use of 1% does raise the eventual vis- 1O g y increases iI1 viscosity a spaced Pfiriod after f cosity tron of the composition which comprises:

(a) an unsaturated polyester formed b condensln Example H at least one dicarboxylic acid cori taining (1, 3%

Following the procedures of Example I polyester resin ethylenic unsaturation with a dihydric alcohol; samples wereprepared using Koplac 200 0 polyester dis- (b) an a,B-ethylenica1ly unsaturated copolymerizable solved in styrene to a 70:30 polyester to monomer monomer; and weight ratio. M-gO and CaO were added respectively and (c) a thickening agent in an amount sufiicient to inthe viscosity changes noted as follows: crease the viscosity of the composition after a spaced TABLE II Percent Percent Viscosity in cps. Sample No. CaO MgO Initial 1 hr. 3 hrs. 5 hrs. 24 hrs. 168 hrs.

1 Million. 2 No thickening.

Example n period of time consisting essentially of a mixture of As a comparison other calcium and magnesium comii i 3 5. a Secqnd salidselected l binations were tested to illustrate the novel and unexi gg mg 0 magneslum OX1 e and Calclum pected eifects noted when the combinations of the inven- 2. The con'lposition of claim 1 wherein said Second salt tion are utilized in contrast to other combinations. The is magnesium Oxide combinations were tested in polyester resin solutions hav- 3 The composition of claim 1 wherein Said Second Salt ing the same constituents as in Examples I and II, The i calcium hydroxide results were as follows: 4. The composition of claim 2 wherein said thickening TABLE III Viscosity in cps. CaO C&(OH)2 MgO Mg(OH)2 Initial 1 week 2 weeks 1 N o thickening. 2 Million.

In no case was the combination of salts better than agent consists essentially of at least 1% by weight of the either salt by itself and in the calcium hydroxide-ma polyester resin composition of said calcium oxide and at nesium oxide tests the combination gave the worst results; least 1.5% by weight of the polyester resin composition either of the salts by themselves yielded better results of said magnesium oxide. than the combination. This is in marked contrast to the 5. The composition of claim 3 wherein said thickening combination of the invention wherein the results obtained agent consists essentially of at least 1% by weight of the by the combination are far superior to that obtained olyester composition of calcium oxide and at least 2% using any of the salts of the novel combinations solely. by Weight of the polyester resin composition of calcium Thus, the invention provides a novel thickening agent hydroxide. combining a know thickeningtagent with a inoperative 6. In an unsaturated polyester resin composition which agent to yield a polyester having improved pot life by has incorporated therein a chemical thickening agent to decelerating the initial thickening rate yet increasing the provide a large increase in viscosity after formation of the overall viscosity gain to provide a much higher viscosity composition which comprises: after about 24 hours. (a) an unsaturated polyester formed by condensing at The invention enables one to chemically thicken a least one dicarboxylic acid containing a,fl-ethylenic polyester resin to rapidly build up the viscosity in several unsaturation with a dihydric alcohol; days without significantly increasing the initial viscosity (b) an a,,8-ethylenically unsaturated copolymerizable or shortening the pot life of the polyester resin as has monomer; and been the case with the chemical thickeners used heretoa h i l thickening agent capable of increasing fore. Fibrous reinforcements can thus be pre-coated with the viscosity of the composition selected from the a low viscosity polyester resin which will therefore propclass consisting of calcium hydroxide and magnesium erly wet the fibers, yet the polyester resin coating will oxide, rapidly lose its tacky state by the increase in viscosity the improvement which comprises: enhancing the storability of the pre-coated fibers. adding at least 1% by weight of the total polyester resin 7 composition of calcium oxide to increase the pot life of the resin by slowing the initial viscosity increase and to raise the overall viscosity obtained after 24 hours.

References Cited UNITED STATES PATENTS 2,568,331 9/1951 Frilette 260865 3,219,604 11/1965 Fischer 260865 8 3,373,129 3/1968 Kori et a1. 260-40 3,390,205 6/1968 Schnell et a1. 260863 2,628,209 2/1953 Fisk 260865 5 MURRAY TILLMAN, Primary Examiner.

J. T. GOOLKASIAN, Assistant Examiner.

US. Cl. X.R. 260-40 

